基二乘FFT,C语言注释
时间: 2023-07-26 14:04:42 浏览: 43
下面是基于C语言的基2乘FFT算法的注释说明:
```
void fft(double *x, double *y, int n) {
int i, j, k;
double c, s, t1, t2;
// Bit-reverse the input array x
bit_reverse(x, y, n);
// Perform the FFT
for (k = 2; k <= n; k *= 2) {
for (j = 0; j < k / 2; j++) {
c = cos(-2 * PI * j / k);
s = sin(-2 * PI * j / k);
for (i = j; i < n; i += k) {
t1 = c * x[i + k / 2] - s * y[i + k / 2];
t2 = s * x[i + k / 2] + c * y[i + k / 2];
x[i + k / 2] = x[i] - t1;
y[i + k / 2] = y[i] - t2;
x[i] += t1;
y[i] += t2;
}
}
}
}
void bit_reverse(double *x, double *y, int n) {
int i, j, k;
double t;
j = 0;
for (i = 0; i < n; i++) {
if (j > i) {
t = x[j];
x[j] = x[i];
x[i] = t;
t = y[j];
y[j] = y[i];
y[i] = t;
}
k = n / 2;
while (k <= j) {
j -= k;
k /= 2;
}
j += k;
}
}
```
注释说明:
- `fft`函数为基2乘FFT算法的主要实现部分,参数`x`和`y`是输入输出数组,`n`是数组长度。
- `bit_reverse`函数用于将输入数组按位反转,以便在FFT计算中使用。